Study Guide: https://quizlet.com/_1e48ro
Concise Notes:
Unit 7 - Cellular Transport Concise NOTES
1. Cell membrane (plasma
membrane)
A.
The
boundary between the cell and its environment.
B.
Allows
nutrients to enter the cell and waste products to leave the cell in order to
maintain homeostasis, the process of maintaining the cell’s environment
in order to survive, a balance between the cell and its environment.
C.
Found in
all cells.
D.
Selectively permeable - allows some molecules to come into the
cell while keeping others out.
2.
Structure
and Function
A.
Fluid-Mosaic Model
1. Fluid
because it is flexible
2. Mosaic because proteins are embedded in
the membrane that make a pattern
B.
The cell
membrane is composed of a phospholipid bilayer, which is two layers of
phospholipids back to back.
1. A glycerol backbone
2. Two fatty acid chains or tail
(a) water-hating or hydrophobic
(b) Helps prevent the cell membrane from
dissolving.
(c) The tails are inside the membranes so they
can stay away from the water.
3. A phosphate group “head”
(a) water-loving” or hydrophilic
(b) Allows the cell membrane to interact with its
watery environment
(c) The polar phosphate heads of the phospholipid
face toward the water that is either inside the cell or outside the cell.
C.
Movement of Materials
1. Small polar and non-polar molecules move free
through the cell membrane.
(a) Water, Oxygen, Carbon Dioxide
2. Charged ions and larger molecules such as
proteins and sugars must be helped through.
(a) Sodium and Calcium ions, sugars, proteins
3. The two layers of phospholipid molecules make
a “Sandwich” with the fatty acid tails forming the interior of the membrane and
the phospholipid heads facing the watery environment outside the cell.
(a) When many phospholipid molecules come
together, a barrier is created that is water soluble at its outer surfaces and
water insoluble in the middle.
Water-soluble molecules will not easily move through the membrane
because they are stopped by this water insoluble layer.
4. Transport
proteins span the entire membrane
and regulate which molecules enter and which molecules leave the cell, allow
needed substances to move into the cell, and waste materials to move out of the
cell through the cell membrane.
D.
Identification: Other proteins and carbohydrates
stick out from the cell surface and help cells identify each other. Some of these are important in protecting
your cells from infection.
E.
Support
Structure: Some proteins
are found only at the inner surface of the cell membrane. They help attach the cell membrane to the
cells internal support structure (cytoskeleton) making the cell
flexible.
3.
Cellular
Transport – the movement of substances move into and out of a cell – 2 types:
Passive and Active
A.
Passive
transport – 3 Types
1. Diffusion is the movement of particles
from an area of greater concentration to an area of lower concentration. This means that molecules move from where
there are a lot of them to where there are only a few molecules.
(a) Concentration Gradient - The difference
in concentration (amount of solute in a given amount of solvent) of a substance
across a space. Because ions and molecules move from an area of higher
concentration to an area of lower concentration, they are said to move with the gradient.
(b) When
there is a higher concentration of molecules outside the cell than inside the
cell, the molecules will move into the cell.
If there is a higher concentration of molecules inside the cell than outside
the cell, the molecules will move out of the cell.
(c) If
no other processes interfere, diffusion will continue until there is no concentration gradient. At this point, equilibrium occurs. This
means there is an equal number of molecules on both sides of the membrane. Therefore, the concentration of a substance
is the same throughout a space.
2. Osmosis is the diffusion of water
across a cell membrane.
(a) In
a cell, water always tries to reach an equal concentration on both sides
of the membrane (dynamic equilibrium).
(b) In
osmosis, water will flow to the side of the membrane where the water
concentration is lower, from the side where the concentration is higher. So, we are still moving from an area of
higher concentration to an area of lower concentration. Osmosis is the same as diffusion, but it is
the water that is moving across the membrane.
(1) Hypotonic – amounts of solute particles
are lower, (water molecules higher)
(2) Hypertonic – amounts
of solute particles are higher (water molecules are lower)
(3) Isotonic – amount of solute particles are equal (Water
molecules are equal)
(c) Cells
in Solutions
(1) Hypotonic solution - water moves into
cell – the cell swells as water moves into the cell
(2) Hypertonic solution - water leaves
cell – the cell shrinks as water moves out of the cell
(3) Isotonic solution - no measureable change
- If you put a cell in an isotonic
solution, the cell will stay the same.
(a) Most solutions are isotonic so that cells are
not damaged by the loss or gain of water.
(d) Turgor
pressure is the pressure within a
cell due to water.
(1) As the pressure increases inside animal
cells, the cell membrane swells. Red
blood cells are an example of this. If
the solution is extremely hypotonic, the cell membrane may be unable to
withstand this pressure and may burst. Cytolysis
occurs when the cell takes in water, swells, and bursts.
(2) Plant cells do not burst when in a hypotonic
solution because of the rigid cell wall. Instead, the plant cell becomes more
firm, or turgid.
(3) Animal cells in a hypertonic solution shrivel
because of decreased pressure in the cells.
Plasmolysis is the loss of turgor pressure due to water
leaving. Animal cells shrivel and plant
cells wilt.
3. Facilitated Diffusion - passive transport of materials across the
cell membrane with the aid of transport proteins
(a) Transport
proteins help substances move
through the cell membrane. These
proteins function to carry molecules across the membrane.
(1) Transport proteins called Channel proteins
provide openings for particles to pass through.
These channels are “gated” so they can open and close, thus regulating
the flow of ions or molecules.
4.
Active transport – Using energy to move particles from a region of lower
concentration to a region of higher concentration to counteract the force of
diffusion that is moving the particles in the opposite direction.
A.
Movement
of materials through a membrane against a concentration gradient is
called active transport and requires energy from the cell.
B.
In
active transport, a transport protein called a carrier protein first
binds with a particle of the substance to be transported. Each type of carrier protein has a shape that
fits a specific molecule.
C.
When the
right molecule binds with the protein, chemical energy allows the cell to
change the shape of the carrier protein so that the particle to be moved is
released on the other side of the membrane.
D.
Once the
particle is released, the protein’s original shape is restored.
E.
Endocytosis is a process by which a cell surrounds and takes in material from its
environment. This material does not pass
directly through the membrane. Instead,
it is engulfed and enclosed by a portion of the cell’s cell
membrane. That portion of the membrane
breaks away, and the resulting vacuole with its contents moves to the inside of
the cell.
1. 2 Types of Endocytosis:
(a) Pinocytosis – movement of liquids
(b) Phagocytosis – movement of large particles.
F.
Exocytosis
- The reverse of endocytosis, the expulsion of materials from a cell.
1. Cells use exocytosis to expel wastes from the
interior to the exterior environment.
They also use this method to secrete substances, such as hormones
produced by the cell.
G.
The Sodium-potassium
pump is an active transport system that allows for muscle contraction.
Comparison of Cellular Transport
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